Loudspeaker assembly



' 7, 1967 H. SCHOENGOLD v LOUDSPEAKER ASSEMBLY 4 Sheets-Sheet 1 Filed Feb. 5, 1964 HERBERT SCHOENGOLD INVENTOR BY J ATTOENEX H. SCHOENGOLD 3,351,719

LOUDSPEAKER ASSEMBLY 4 Sheets- Sheet 2 Nov. 7, 1967 Filed Feb. 5, 1964 HERBERT SCHOENGOLD INVENTOR.

BY W Afragygr 7, 1967 H. SCHOENGOLD 3,351,719

' LOUDSPEAKER ASSEMBLY Filed Feb. 1954 4 Sheets-Sheet 3 H m I WHEEW Fla.

'. 1 Yo HERBERT SCHOENGOLD M1154" =INVENTOR.

404 as 7 FIG 5.

- ATTUENEY Nov. 7, 1967 H. SCHOENGOLD LOUDSPEAKER ASSEMBLY 4 Sheets-Sheet 4 Filed Feb.

,IIIIIIIA I H ER BERT SCHO ENGOLD INVENTORQ Y We ATTORNEY United States Patent Filed Feb. 5, 1964, Ser. No. 342,827 18 Claims. (Cl. 179-1155) I ABSTRACT OF THE DISCLOSURE,

Thin light weight sound reproducing equipment comprising a substantially flat marginal frame, a substantially 3,351,719 Patented Nov. 7, 1967 ice - diaphragmmay all be molded or formed of the same a material and constructed as a single integral unit.

fiat diaphragm secured at its peripheral edges only to the frame, a voice coil mounted on the diaphragm, a magnet surrounding the voice coil and supported by a magnet supporting rib extending substantially parallel to the diaphragm and spaced therefrom, the frame, diaphragm, and magnet supportingrib all being formed of cellular plastic material;

This invention relates to sound reproducing equipment such as loudspeakers and the like which are light in weight, economical to produce, and which possess im-. proved acoustical characteristics. The invention is directed particularly to constructions wherein a novel type of frame is provided for supporting a diaphragm and characteristics of the diaphragm. Thus, they may be made of metal, plastic, Wood or other material which are in' no way related to the properties or characteristics of the diaphragm and other moving parts. The diaphragm then must be mounted in resilient or yielding supports and provided with compliance elements or other flexible means in order to separate or isolate the diaphragm acoustically from its supporting structure. However, in spite of the use of such compliances or flexible mounting means for the diaphragm and the magnet, voice coil or other elements, of the assembly, objectionable resonant or interfering acoustical effects may be developed which limit the frequency range or result in distortion of the sound waves produced by the equipment. Moreover, the disparity in physical properties of the frame or mounting means and the diaphragm frequently give rise to changes in the functional characteristics of the equipment and limitthe usage thereof due to differences in thermal expansion, the action of moisture, and other conditions which may alter the dimensions or change the properties of the elements.

In accordance With the present invention, these ObjCC'. tions and limitations of prior constructions are reduced or eliminated and assemblies are provided wherein the frame, basket or mounting means is constructed and designed to reduce acoustical interference. In the preferred embodiments of the present invention the edges of the diaphragm are fixedly secured to the frame, basket or mounting means by which it is'supported and the frame and diaphragm are formed of materials which possess similar, related or matching physical properties. In fact,

In a typical assembly embodying the present invention the frame is formed of or embodies light, but strong, expanded cellular plastic material such as polystyrene, or other cellular type material or material having similar acoustical characteristics while possessing substantial strength and stiffness. The diaphragm as well as the elements bywhich the voice coil and magnetic elements are supported may also be formed of or embody cellular plastic material such as polystyrene or it may be formed of other material differing in composition from the frame but possessing properties which are related or acoustically matched to those of the frame. Constructions of this type have further advantages in that they are extremely light in weight, resistant to the action of moisture and temperature changes, economical to produce, and, if desired, the frame, diaphragm and magnet supporting elements can all 'be molded together in a single operation.

Accordingly, the principal object of the present invention is to provide a novel type of sound reproducing equipment embodying a frame or. support which possesses improved physical and acoustical properties which may be the same or related to those of the diaphragm and other relatively movable elementsof the assembly.

Another object of the invention is to increase the range and improve the fidelity of the sounds produced and to decrease undesired resonant effects developed upon operation of the sound reproducing equipment.

A further object of the invention is to provide a loudspeaker assembly which is extremely light in weight while being strong and resistant to the action of temperature changes and moisture conditions. I

A specific object of the invention is to providesound reproducing equipment embodying a frame and/or other elements adapted to be secured to or formed integral with the frame and composed of molded expanded cellular plastic material. I i

These and other objects and features of the present invention will appear from the following description thereof wherein reference is made to the figures of the accompanying drawings.

" In the drawings:

FIG. 1 is a perspectiveillustrating a typical form of loudspeaker assembly embodying the present invention;

FIG. 2 is a rear elevation of the loudspeaker frame, diaphragm and voice coil assembly;

FIG. 3 is a sectional view through the assembly illustrated in FIG. 2 taken on the line 33 thereof;

FIG. 4 is a sectional view through a portion of the frame assembly of FIG. 1;

FIG. 5 is a sectional view of a modified form of the present invention; I

FIG. 6 is a sectional view through typical elements employed in producing the construction of FIGS. 2, 3 and 4;

FIG. 7 is a rear elevation illustrating an alternative embodiment of' the present invention;

FIG. 8 is a sectional view of the construction shown in FIG] taken on the line 88 thereof;

FIG. 9 is a rear elevation showing a further embodiment of the present invention; and

FIG.'10 is a sectional view illustrating a further alternative embodiment of the present invention.

In that form of the invention chosen for purposes of v v illustration in FIGS. 1, 2 and 3 of the drawings, the loud- 'speaker assembly embodies a diaphragm 2 formed of erably is substantially fiat inform and may be molded,

' integral with a frame 4 which extends about the marginal edges of the diaphragm. The diaphragm 2 and the frame 4 are shown as being generally rectangular in shape whereby the piston area of the diaphragm is substantially greater in area than that of a conventional circular diaphragm. The frame is substantially thicker than the diaphragm and may be formed of acoustically compatible polystyrene or other plastic material which is somewhat denser than that used in forming the diaphragm 2. The frame is provided with central magnet mounting ribs 6 which extend across the frame and are arranged to receive and mount the magnetic element 8 of the loudspeaker assembly. Diagonal reinforcing ribs 10 may also be provided; and, if desired, other suitably positioned strengthening and reinforcing ribs or inserts may be provided and molded integral with the frame when the assembly is relatively large.

As shown in FIGS. 2 and 3, the diaphragm 2 extends from the inner edge of the lower horizontal frame member 12 to the inner edge of the upper horizontal frame member 14. In a similar way, the diaphragm 2 extends from the inner edge of the vertical frame member 16 at one side of the frame 4 to the inner edge of the vertical frame member 16 at the opposite side of the frame. On the other hand, the central portion of the diaphragm 2 is spaced from the central magnet mounting ribs 6 and the diagonal bracing ribs 10 so as to be fixedly mounted adjacent its edges while being free to vibrate at the center and with respect to the magnetic element 8 mounted on the central ribs 6.

The voice coil 18 of the loudspeaker assembly is securely mounted on a voice coil form 20 which preferably consists of a thin, lightweight insulating tube made of plastic coated paper or the like. The voice coil form 20 is fixedly secured to the diaphragm and is preferably embedded in the molded material of which the diaphragm is formed. A reinforcing plate 22 is also embedded in the diaphragm 2 and fits closely about the voice coil form 20 and may be bonded or cemented thereto or formed integral with the voice coil form so as to secure the form 20 and the voice coil in fixed positions with respect to the diaphragm. Furthermore, the electrical leads 24 connected to the voice coil 18 are preferably embedded in the material of which the diaphragm is formed so as to be held fixedly in place preventing damage thereto or relative movement thereof during vibration of the diaphragm. The ends 26 of the leads 24 may extend out through the frame 4 at the edge of the diaphragm and are connected to a terminal member or jack 28 mounted on the frame or partially embedded therein for ease of connection with an actuating circuit of any type. If desired, the leads 24 may further be folded back upon themselves as indicated at 30 while embedded in the material of which the diaphragm is formed, whereby they afford a measure of movement sufficient to eliminate any restriction to the movement of the diaphragm. However, relative movement of the lead-in wires is prevented so that no electrical or induced interference will be developed and undesired noise, buzz and mechanical disturbance is eliminated.

The reinforcing plate 22 preferably extends radially outward from the coil form 20 for a considerable distance, say several inches, and is preferably provided with openings 28 therein to permit the flow of the material of which the diaphragm is formed through such openings to anchor the reinforcing plate and the voice coil form securely in place. In order further to reinforce and strengthen or stiffen the central portion of the diaphragm 2 and prevent possible rupture thereof adjacent the voice coil form due to the impact of the vibrations and forces applied thereto, additional centrally located sheets or layers of strong thin material 30 may be applied to the opposite faces of the diaphragm about the voice coil. If desired, the diaphragm may also be thickened somewhat adjacent the center as shown at 32 and the reinforcing sheets 30 may be applied over such thickened portions as shown or embedded therein.

The reinforcing plate 22 and the reinforcing sheets 30, when employed, may be formed of any suitable strong lightweight material. Thus, the reinforcing plate 22 may be formed of a compressed, plastic-impregnated, fibrous material, whereas, the sheets 30 may be formed of strong plastic sheet material such as polyvinyl chloride, polyvinyl acetate, plastic impregnated paper or fabric, metal foil or other suitable material.

The diaphragm 2 is formed of a cellular or expanded plastic material which is relatively hard and stiff and very light in weight. One preferred material employed in producing the diaphragm is expanded or cellular polystyrene which may be molded from individual beads of foamed polystyrene by the action of heat and pressure. The density of the molded material used in forming the diaphragm should be within the range of about 0.8 to 10 pounds per cubic foot depending upon the size of the diaphragm and the power employed in actuating the sound reproducing equipment. It should be as light as possible while possessing the requisite stiffness and strength. Polystyrene diaphragms which are from about to /2 inch or more in thickness and have a density of about 1 to 1.8 pounds per cubic foot are preferred. The material employed in molding the frame also should, of course, be stiff, strong and substantially rigid and may also consist of or embody expanded cellular polystyrene. While the strength and stiffness of the frame will inherently be greater than that of the diaphragm because of its greater thickness, the material used in forming the frame may also have a greater density than that of the diaphragm.

The diaphragm, when formed, presents a substantially smooth outer surface and possesses the desired stiffness or rigidity to provide the requisite piston effect for generating undistorted sound waves with a minimum of displacement of the diaphragm. Although the surface of the diaphragm may have a continuous molded skin thereon or be provided with a sealing coat or layer of hard lacquer or the like to increase the smoothness and hardness thereof, such a skin or layer is not desirable. It is found advantageous to remove the surface layer formed during the molding operation by the application of a solvent or by abrasion of one or both faces of the diaphragm.

When the sound reproducing equipment is designed for use in the midor high frequency range, it may be of substantially uniform thickness throughout the area thereof. Nevertheless, when fidelity in low frequency ranges is desired, the diaphragm 2 may be provided with a plurality of grooves or compliance zones 36 extending about the central piston area 38 of the diaphragm as shown in FIG. 5. The central stiff piston area 38 should, nevertheless, occupy 50% or more of the entire area of the diaphragm. With such constructions, it is found that the loudspeaker is capable of reproducing an extremely wide band of sound frequencies ranging from about 20 to 20,000 c.p.s. without material distortion.

The frame and diaphragm assembly thus provided presents no abrupt or sharp discontinuity in the physical and acoustical properties thereof whereby reflex or parasitic vibrations emanating from the frame or marginal portions of the diaphragm are eliminated or reduced to a minimum, whereas, the full piston effect of the entire diaphrgam may be attained. Furthermore, because of the cellular nature of the material preferably used in forming the frame, it tends to absorb vibrations and has no inherent resonant frequency which would tend to reflect or feed back undesired and interfering vibrations to the diaphragm even though the diaphragm is fixedly secured thereto.

Another feature of the assemblies embodying the present invention resides in the open or exposed rear or inner surface of the diaphragm whereby both the front and the rear of the diaphragm serve as sound propagating surfaces. In t-he preferred forms of the invention, the inwardly facing surfaces of the frame members 12, 14 and 16 and the opposite sides of the central ribs 6 and bracing ribs thickness of the assembly in adirectionnormal to'the' diaphragm can be extremely limited whereby a very thin construction can be provided. Loudspeakers having outstanding acoustical 'characteristicsbut which are only a 7 little over one. inch in thickness andcxtremely light in weight can be produced in this way. Such speakers are particularly suitable for use in portable equipment such as radios and. television sets but can also be used by themselves or in standard base or reflex types of cabinet 7 structures. Theycan further be used in baffled speaker" equipment particularly when better low frequency response is desired. When therframe and diaphragm are formed of non-hygroscopic polystyrene or other expanded cellular plastic material, they also are substantially un affected by moisture and. wide changesin temperature so as to be useful in equipment employed outdoors in marine applications, swimming pools, or as permanent installations in stadiums, ball parks and elsewhere.-

The frame 4 and other elements of the assembly can be mounted as shown in FIGS. 1 and 4' in a decorative support such as an upright, horizontal orportable mounting unit 33. The unit 33 illustrated, embodies channel members 35 which may have rubber or other cushioning strips 37 carried thereby to hold the frame 4 of the loudspeaker in place without causing undesiredvibration, of the support. Further, if desired, bolts 39 or the like may extend through the unit 33 adjacent the corners thereof and through washer 41 or the like embedded in or carried by the frame 4 of the loudspeaker forholding the speaker assembly in place within the unit. The construction thus provided allows the frame to be properly mounted and permits limited compression of the cellular plastic material to occur when securing the speaker assembly in a unit Without danger of distorting or twisting the frame 4 or the diaphragm 2. Sound distortion due to the twisting or unequal strains placed on the edges of the diaphragm therefor is eliminated. 1 V I Alternatively, if the mounting to the decorative support or cabinet enclosure is such so ,that unWanted vvibrations do not occur, the channel members such 215 34" and cushioning strips 36 maybe eliminated and the grill clothmounted flush with the molded frame. so as to provide minimum thickness for the final speaker assembly.

The magnetic element 8 of the loudspeaker assembly forms a part of a magnet assembly 42 which is carried by the magnet supporting ribs 6 of the frame 4. The element 8 may be formed of any suitable material such as'the magnetic alloy Alnico, if desired. However, it is preferable to employ a magnetic element formed of ceramic material, such as that known to the trade as Indox, for the purpose of obtaining. the thinnest possible structure. The magnet assembly is provided with a central pole piece 44, a bottom plate 46 and a top pole piece 48 formed of ferromagnetic material. The central pole piece 44 and top pole piece 46 present parallel surfaces which are spaced apart to provide an air gap 50 in which the voice coil 18 on voice coil form is located. The outer periphery of the magnetic element 8 preferably projects outward beyond the top and bottom plates 46 and 48 and is embedded in the foamed plastic or polystyrene of which ribs 6 are formed to assure proper positioning and rigid mounting of the magnet assembly 42 with respect to the voice coil and coil form carried by the diaphragm 2. The outer faces of the top and bottom plates 46 and 48 can then be flush with the'opposite faces of the magnet mounting ribs 6.

With this construction, a magnetic assembly providing the desired magnetic flux in the air gap 50 can be provided while maintaining the whole magnetic assembly relatively thin and light in weight. Moreover, the relative positions of the magnet and voice coil can be positively and permanently fixed with the utmost accuracy and held against subsequent undesired relative movement which might, result in sound distortion or' improper operation of the diaphragm or speaker. In fact, an air gap of only a few thousandths of an inch radial clearance can, thus,

he provided, and the power requirements for actuating the sound reproducing equipment can be reduced. Furthermore, the molding or embedding of the coil form directly in. the material of the diaphragm and the molding or embedding of the magnetic assembly in the ribs 6 of the frame precludes possible misalignment thereof with re! spect to each other. 1

Accuracy in the positioning and centering of the voice coil and magnetic elements with respect to each other canbe assured as shown in FIG. 6 by employing a cylindrical locating member 52 which is mounted in a mold 54 and provided with a centering pin 56. The reinforc ing plate 22 and the voice coil form 20 with the voice coil 18 thereon can then be fitted over the locating member 52 so as to be accurately positioned and held thereby.

The magnetic assembly is placed in position and centered curacy. After the molding operation is completed and the parts are secured in place, the loudspeaker assembly may be withdrawn from the mold andlocating member 52 and a plug of foamed plastic material 58 can be cemented in place in the diaphragm to cover the opening through V which the centering member extends as shown in FIG. 3. The construction thus. provided is characterized by the fact that the diaphragm and the frame are formed of the same or similar compositions and will be. affected in a like manner by temperature changes, moisture and other conditionssto which the equipment may besub-v jectedduring'use. As a result, it serves to prevent distortion, tilting or the development of eccentricity of the voice scoilzwithin the airgap and electrical, magnetic and acoustical distortion are eliminated. Thepower required to actuatethe'equipmentcan, therefore, be reduced whereas the tone and quality of the sounds produced'are improved,

. and the sensitivityof the loudspeaker is increased.

While the construction 'shown andtdescribed with reference to FIGS. 1 to 4 and 6 of the drawings has many advantages, it is sometimes desirable to form the frame and diaphragm separately as shown in FIG. 5. The frame 60 then may be molded separately or otherwise formed of material of relatively high density or different compositions whereas the diaphragm 62 may be formed separately by other molding, forming, cutting or fabricating operations and from any suitable or preferred material having the requisite density. The edges of the diaphragm are then cemented or otherwise secured to the frame so as to be fixedly attached to the shoulders 64. The outer edges of the diaphragm preferably abut the inwardly facing surfaces 66 on the frame so as to aid in positioning and holding the diaphragm and the voice coil carried thereby in fixed positions with respect to the magnetic assembly employed in the sound reproducing equipment.

Such diaphragms may be provided with compliance zones or groove 36, if desired; and, in fact, the diaphragm can be made of any appropriate material having the desired properties for effective sound reproduction. In any such assembly, the sound absorbing and non-resonant characteristics of the frame will eliminate the reflex and interfering vibrations which would otherwise be transmitted to the diaphragm from the frame by reason of the fixed attachment of the diaphragm to the frame. It is,

nevertheless, preferable to use materials in forming the frame and diaphragm which possess similar physical properties so that the disparity in such properties in the zone of attachment of the diaphragm to the frame will be relatively limited.

In those embodiments of the invention wherein the over-all weight of the assembly is not of importance or extreme ruggedness is required, the central reinforcing and magnet mounting ribs employed may be formed of metal or other suitable material, hard resinous material or the like. Thus, as shown in FIGS. 7 and 8, a central web 70 may be provided and have its opposite ends 72 embedded in or otherwise secured to the frame 74. The mid-portion of web 70 may be provided with a mounting ring 76 to which the magnet 78 and pole pieces 80, 82 and 84 can be secured and held in place by bolts 86 and 88 or otherwise. In a similar way, the entire frame or those parts thereof which are subjected to greatest strain or used in mounting the equipment on a support may be provided with metal or other members which are at least partially embedded and molded into the material of which the frame is formed.

In the construction illustrated in FIG. 9, such a rigid metallic or similar element 90 is provided and formed with diagonally extending arms 92 connected to a marginal reinforcing rim 94 embedded in or mounted in a frame or unit 96. A heavily reinforced assembly of this type may be provided with a plurality of magnet assemblies 98 and voice coil forms 1% secured to a single diaphragm 102 near the central portion of the diaphragm. The voice coils associated with the various magnet assemblies can then be connected in series-parallel arrangements or otherwise to produce an increased sound output or to provide improved impedance matches. Such equipment is particularly adapted for use in sirens, fog horns, public address systems or other high powered sound reproducer.

In that form of the invention illustrated in FIG. 10, the assembly is capable of use outdoors or under conditions wherein it may be subjected to excessive amounts of moisture such as rain, heavy fog or even under water. For this purpose, the magnetic element 110 is surrounded by a retaining ring 112 and is provided with a plastic or other sealing cover 114 which extends over the rear face of the magnet assembly and is sealed to the retaining ring 112 to provide a moisture-proof enclosure for the magnet assembly. An accordion-like or pleated sealing element 116 formed of rubber, plastic or other durable soft and yieldable material surrounds the voice coil form 118 and may be sealed to or molded integral with the diaphragm 120 and the retaining ring 112. The magnet assembly with its enclosure may be supported from the frame 122 by plastic or metal ribs or a web 124 so as to hold the magnet and voice coil in fixed relative positions.

With this construction, the outer end of the voice coil form 118 is closed by a plastic or other sealing and reinforcing sheet 128 whereas the impervious nature of the foamed plastic material employed in forming the diaphragm serves to protect the electrical elements and voice coil lead wires 130 from contact or damage by water or moisture. At the same time, the flexible character of the pleated sealing element 116 permits free movement of the diaphragm and eliminates objectionable damping of the diaphragm movement due to compression of air enclosed between the diaphragm and voice coil form during operation of the speaker. Moreover, if desired, the space in which the voice coil and magnetic assembly are enclosed may be evacuated if desired.

In each of the forms of the invention described, the extended piston effect of the diaphragm is attained whereas its extremely light weight renders it possible to actuate the diaphragm with a minimum of power and renders it highly sensitive and responsive to fluctuations in the current supplied to the voice coil.

While those embodiments of the invention chosen for purposes of illustration and described above are characterized by their thin flat form, the invention is also adapted for use when employing a cone or other shape or type of diaphragm and a frame, basket or support of conventional shape or form and of much greater depth than those illustrated.

A further and important feature of the present invention which characterizes each of the forms thereof is the simplicity of construction which renders it possible to form the diaphragm, as well as the reinforcing and coil Supporting ribs and frame, as a unitary construction or with the desired inserts by the use of molding equipment and as a simple high speed operation.

Accordingly, it is possible to produce improved loud speaker assemblies of various sizes and types possessing outstanding tone qualities and ranges of frequency which are extremely light in weight and capable of use in a great variety of applications. In view thereof, it should be understood that the particular embodiments of the invention shown in the drawings and described above are intended to be illustrative only and are not intended to limit the scope of the invention.

I claim:

1. A loudspeaker assembly comprising a substantially flat diaphragm, a marginal frame which is acoustically compatible with the diaphragm, said frame being contacted by said diaphragm at only the peripheral edges of the diaphragm, the diaphragm and frame both being formed of stiff cellular plastic material.

2. In a loudspeaker a diaphragm, and a frame supporting the diaphragm adjacent the periphery only of the diaphragm thereof, said diaphragm and frame being a unitary structure composed substantially entirely of stiff cellular plastic material.

3. A loudspeaker assembly comprising a diaphragm, a frame which is acoustically compatible with the diaphragm, said diaphragm contacting the frame throughout the edges only of the diaphragm, the diaphragm and frame both being formed of stiff cellular polystyrene.

4. In a loudspeaker a diaphragm, and a frame supporting the diaphragm adjacent the periphery only of the diaphragm thereof, said diaphragm and frame being a unitary structure composed substantially entirely of cellular polystyrene.

5. A loudspeaker assembly as defined in claim 1 wherein magnet supporting means are connected to said frame and extend substantially parallel to said diaphragm in spaced relation thereto, a voice coil form carried by said diaphragm and projecting therefrom toward said magnet supporting means, and a magnet carried by said magnet supporting means and having a pole piece thereon surrounding said voice coil form.

6. A loudspeaker assembly as defined in claim 1 wherein magnet supporting means formed of molded plastic material integral with said frame extend substantially parallel to the diaphragm and are spaced from the diaphragm, a voice coil form mounted on the diaphragm and extending toward the magnet supporting means, and a magnet is molded on said supporting means and has a pole piece surrounding said voice coil form.

7. A loudspeaker assembly as defined in claim 1 wherein the diaphragm has substantially fiat front and rear faces and the frame is provided with reinforcing ribs spaced from the rear face of the diaphragm, the frame and reinforcing ribs being provided with lateral walls inclined outwardly from the rear face of the diaphragm at an angle of about 30 to 45 with respect to the rear face of the diaphragm.

8. A loudspeaker assembly as defined in claim 1 wherein a voice coil form is mounted on said diaphragm, a voice coil is supported on said voice coil form, and electrical conductors extend from said voice coil to the marginal portion of the diaphragm and are secured throughout the major portion of the length thereof to the material of which the diaphragm is formed.

9. A loudspeaker assembly as defined in claim 1 wherein a voice coil form is mounted on said diaphragm, a voice coil on said voice coil form, and electrical conductors extend from said voice coil to the marginal portion of the diaphragm and embedded throughout the major portion of the length thereof in the material of which the diaphragm is formed.

10. A loudspeaker assembly comprising a diaphragm formed of cellular plastic material, a voice coil form carried by said diaphragm, a voice coil on said voice coil form and electrical conductors extending from said voice coil to a point adjacent an edge of the diaphragm and embedded in the diaphragm.

11. A loudspeaker assembly as defined in claim 10 wherein the electrical conductors are folded back and forth within the material of which the diaphragm is formed.

12. A loudspeaker assembly comprising a substantially flat diaphragm and a substantially flat frame to which the marginal portions only of the diaphragm are fixedly secured, the frame and diaphragm being formed of materials which possess similar acoustical properties.

13. A loudspeaker assembly oomprising a substantially flat diaphragm, a voice coil form fixedly secured to said diaphragm adjacent the center thereof, a frame extending about the edges of said diaphragm and contacting the peripheral edges only of said diaphragm, magnet supporting means having its opposite ends fixedly connected to said frame, said magnet supporting rib extending generally parallel to said diaphragm, a voice coil mounted on the voice coil form, a magnet assembly carried by said support and having a pole piece surrounding said voice coil, the diaphragm, frame and magnet supporting means all being formed of stiff cellular plastic material.

14. A loudspeaker assembly as defined in claim 13 wherein a reinforcing member is embedded in the dia phragm and said voice coil form is fixedly connected to said reinforcing member.

15. A loudspeaker assembly as defined in claim 13 wherein at least 50% of the area of the diaphragm adjacent the center thereof and surrounding the voice coil form presents unbroken flat surfaces.

16. Sound reproducing equipment comprising a frame, a diaphragm and means for energizing said diaphragm, the edges only of said diaphragm being fixedly secured to said frame, and said frame and diaphragm having similar physical properties.

17. Sound reproducing equipment comprising a frame formed of molded cellular plastic material, a diaphragm having its edges only secured to said frame and means for energizing the diaphragm.

18. A thin, light weight, sound reproducing device embodying a marginal frame formed of a molded body of cellular plastic material, a diaphragm formed of stiff, cellular plastic material having its marginal edge secured to said frame near one face of the frame, a voice coil form secured to said diaphragm and located near the center thereof, said voice coil form projecting from the diaphragm toward the opposite face of said frame, a voice coil on said projecting portion of the voice form, a magnet mounting rib positioned in spaced parallel relation with respect to said diaphragm and secured to said frame near said opposite face of the frame, and a magnetic element for actuating said voice coil and diaphragm carried by said magnet mounting rib and surrounding said voice coil.

References Cited UNITED STATES PATENTS 1,918,422 7/1933 Nystrom 181-32 2,124,834 7/1938 Stenger 181-32 2,396,825 3/1946 Burroughs 181 32 2,789,161 4/1957 Brennan 179-1155 3,143,183 8/1964 Herbstman 1s1 311 3,172,498 3/1965 Gorike 181-32 3,236,958 2/1966 Cohen 179115.5 3,284,581 11/1966 Fender 179115.5

FOREIGN PATENTS 1,326,414 4/ 1963 France.

KATHLEEN H. CLAFFY, Primary Examiner.

A. A. MCGILL, Assistant Examiner. 

2. IN A LOUDSPEAKER A DIAPHRAGM, AND A FRAME SUPPORTING THE DIAPHRAGM ADJACENT THE PERIPHERY ONLY OF THE DIAPHRAGM THEREOF, SAID DIAPHRAGM AND FRAME BEING A UNITARY STRUCTURE COMPOSED SUBSTANTIALLY ENTIRELY OF STIFF CELLULAR PLASTIC MATERIAL. 